Vacuum cooler



July 5, 1932. H. B, CALDWELL 1,

VACUUM pooLER- Filed Au 16, 1928 VACUUM a PUMP I/Mmtor: 4%arold B Calm/fell Patented July 5, 1932 UNITED STATES PATENT OFFICE- HAROLD B. CALDWELL, OF MOUNT VERNON, NEW YORK, ASSIGNOR TO SWENSON EVAPORATOR COMPANY, OF HARVEY, ILLINOIS, A CORPORATION OF ILLINOIS VACUUM COOLER Application filed LIl'lfit 1C, 192'. Serial No. 299,955.

My invention relates to a vacuum cooler and it pertains more particularly to a vacuum cooling system as applied to a crystallizer.

The solubility of most substances decreases with a decrease in temperature and crystallization is eifected by lowering the temperature of a saturated solution. The size and purity of the crystals is somewhat dependent upon temperature and upon the agitation of the solution, and it is desirable and sometimes essential in a crystallizing system to have these variables easily controllable. My invention relates to a cooling or crystallizing process in which the temperature of the incoming saturated solution is materially reduced to a desired point, in which the vapor is removed by a vacuum system and in which the crystals may be either continuously or intermittently removed.

One of the objects of my invention is to.

provide an improved method or process for cooling liquids,one particularly although not exclusively adapted for the production of crystals from solutions.

Another object is to provide an improved vacuum cooler of the type described.

A further object is to provide a system in which the vacuum serves the double function of removing solvent from the solution and of maintaining the solution at a low temperature.

A further object is to utilize a vacuum for obtaining a low temperature. whereby the heat of vaporization extracted from the solution makes possible a lower temperature than could be obtained by heat exchange methods with a cooling medium of the same temperature. This offers the following advantages over an ordinary cooling water heat ex- .change system :-it avoids a tendency for crystals to form on the walls of the cooler to impede heat transfer; it eliminates the necessity for scrapers, ,or other mechanical devices to remove the crystals from cooling walls and thereby makes it possible for soft materia s such as lead or rubber to be used as a lining for crystallizers;.it provides a temperature lower than that of the cooling fluid without the use of ordinary mechanical refrigeration; it simplifies the apparatus and I makes it possible to provide an inexpensive construction for handling corrosive solutions.

A further object of my invention is to provide a cooling and a crystallizing system in which the temperature may be easily controlled.

A further object is to provide a system which will handle large quantities of solution and which can be absolutely continuous in operation.

- A further object of my invention is to reduce the cost of installation and operation, i

to simplify the manipulation and to obtain crystals of greater uniformity.

Other objects will be apparent as the detailed description of my invention proceeds.

In the accompanying drawing I have shown a preferred embodiment of my invention. In describing this embodiment and its operation I will refer to actual temperatures and pressures but it'is understood that this description is illustrative only and that I am not limited to any of the details herein set forth except as defined by the appended claims.

The invention may be briefly described as a tank provided with a conical bottom having avalved tube extending downwardly therefrom for removing the crystals, the length of the tube being dependent on the vacuum in the tank. The top of this tank leads to a coinpressor for removing the condensable vapor and air. The compressor discharges into a condenser for liquefying the compressed "apor. A vacuum pump maintains the pressure in the condenser at a desired value, and this vacuum pump may be relatively small because it handles only the airand incidental non -condensable gases which are admitted to the system with the solution or through a bleeder valve.

A single figure of the drawing represents a front elevation partly in section of an apparatus embodying the invention.

A tank 4 is represented containing a liquid solution 5 which may be introduced into the tion into the tank. The liquid solution may.

comprise any suitable solution such as a solution in which the solvent is water and the solute any suitable substance which is soluble in water. Ifthe solution is corrosive, the interior of the tank 4 may be provided with a lining 8, such as rubber, lead or other suitable material, depending upon the nature of the solution, to prevent corrosion thereof.

A pipe 9 leads from the top of the tank to a compressor 10 of any suitable desi which is capable of maintaining the desire reduced pressure in the space above the liquid solution in the tank. The lower part of the tank forms a cone 13, which connects to a long pipe 14 extending into a receptacle 15 in which the end of the pipe is submerged in liquid. The length of pipe 14 will depend upon the specific gravity of the liquid to be cooled and the pressure in the tank. If a liquid solution is used in which the solvent is water, the pipe should be substantially feet long, allowing for several feet of liquid in the tank.

Suppose a water and salt solution is introduced into the tank at a temperature of 75 degrees Fahrenheit. Since water vapor is continuously removed, there will be rapid evaporation and a consequent decrease in temperature, and since the container is made of a material which is a poor heat conductor the heat of vaporization will be extracte from the solution. The resulting cooling of the solution together with the evaporation of the solvent causes a crystallization of the solute and the crystals, settling to the bottom, pass by gravity through pipe 14 into receptacle 15. The diminished supply of liquid solution in the container may be continuously replenished by a regulated flow of the solution through pipe 6.

The density and temperature of solution 5, if desired, may be kept uniform by an agitator 11, operated from any suitable source of power, whose action may be su plemented by a bleeder valve 12 at the base of the container, for allowing air to percolate through the solution.

The admission of air into the tank throu h valve 12 increases the vaporization of t e solution by increasing its exposed area and by its resulting agitation. By admitting a small amount of air it is ossible to maintain a given temperature with a lower vacuum due to the fact that it would reduce the percent age partial pressure of the water vapor. With the bleeder valve closed, a temperature of about 38 degrees F. may be attained with a pressure in tank 4 of about 5.9 mm. of mercury.

Vapors are withdrawn from tank 4 by compressor 10, which compresses the vapors to a pressure at which their saturation temperature is above the temperature of the cooling medium available (about mm. of mercury in the specific illustrative example) and transfers them to condenser 17.

The condenser may comprise a cylindrical container 18 having a coiled pipe 19 therein, through which water at ordinary temperatures is circulated,for purposes of illustration, say in the neighborhood of 80 degrees Fahrenheit. As the compressor transfers the vapors from the tank to the condenser and the pressure of the vapors is raised to 45 millimeters by the compressor, the temperature of the vapor increases from 38.4 degrees Fahrenheit to 97 degrees Fahrenheit. At this pressure the vapors may be condensed by circulating water at 80 degrees Fahrenheit through coil 19 of the condenser.

In order to facilitate removal of the condensate from the condenser, the lower end thereof is provided with a pipe 21, which extends into a liquid container 22 in which pipe 21 is submerged under a liquid. The pipe is made of such length that the column of condensed liquid therein is sufiicient to overbalance the pressure in the condenser.

The purpose of cooling and condensing the vapor at reduced pressure is to avoid the necessity of handling all of this vapor in the vacuum pump. By the expedient above described, the pump has to handle only noncondensable gases such as air and a minimum of energy is required. Also the installation cost is reduced and the system is more easily controlled.

' By substantially eliminating the water vapor before the actual pumping process begins I avoid the necessity of compressing these vapors to 760 mm. and I avoid the heat losses that would accompany this compression. The hydrostatic column of water associated with the condenser provides a convenient means for transferring the condensed liquid at 45 mm. pressure to atmospheric pressure of 760 mm. without the expenditure of power.

Compressor 10 may be omitted from the apparatus in which case the pressure in the condenser and in the container will be equal. The refrigerated medium used in the condenser must then be colder than the vapors in the container so that the vapors will be condensed and removed from the system prior to the pumping step.

Although the process and illustrative apparatus have been particularly described in conjunction with continuous feed of liquid and delivery of crystals they are suited for intermittent or batch work as Well. The 0111 difference is that in batch working, a (fiasired quantity or char e of the liquid to be treated will be inject into the system and, without the addition of new liquid, the process carried on until the batch is fully. treated.

Having illustrated and described the nature and embodiments of my invention, what I claim and desire to secure by United States Letters Patent is as follows:

1. The method of crystallizing the solute of a liquid solution by cooling-the liquid by means of a cooling medium that is not cool enough directly to effect the cooling, which consists in sub ecting the liquid to a reduced pressure to extract vapor therefrom and thereby cool the same, compressing the vapors to a. pressure that raises their temperature above the temperature of the cooling medium, and subjecting the compressed vapors to the cooling action of the cooling medium.

2. The method of crystallizing the solute of a liquid solution by cooling the liquid by means of a cooling medium that is not cool enough directly to effect the cooling, which consists in subjecting the liquid to a reduced n-essurc to extract vapor therefrom and thereby cool the same, compressing the vapors lo a pressure that raises their temperature above the temperature of the cooling medium, subjecting the compressed vapors to the cooling action of the cooling medium, and introducing into the vapor before compression a gaseous substance which is essentially inert with respect to the liquid being crystallized to decrease the ratio between vapor pressure and absolute pressure to assist in cooling the liquid.

In witness whereof, I hereunto subscribe my name this 10th day of August, 1928.

HAROLD B. CALDWELL. 

